Modern electronics rely on solid state materials and semiconductors, in particular. However, plasma-based electronic devices assumed a significant role in communications and display systems in the first half of the 20th century. Vacuum tubes were previously used to amplify and switch signals, but have been largely replaced by solid state devices. Vacuum tubes continue, however, to be employed in specialized applications such as in the final amplifier of high power radio transmitters.
Macroplasma devices have also been used in older communications and display systems. One example is the plasma electron tube (such as the OA, OB, OC, and OD series of rare gas-plasma voltage regulators) that was widely incorporated into audio equipment as well as the power supplies of RF transmitters and receivers. Other examples include plasma switches and the 866A and 872 mercury plasma high voltage rectifiers that found application in early RF transmitters. Another example is the Nixie tube, a neon plasma based device that was an essential component of alphanumeric displays for a number of decades in the twentieth century.
Subsequent applications of plasmas to electronics or displays have often required imposing external voltages or magnetic fields so as to influence the electromagnetic field distribution in the plasma. For example, U.S. Pat. No. 5,765,073 discloses a field controlled plasma discharge display element serving as a light source element in plasma discharge electrostatic printers. The display element includes a pair of discharge electrodes and a third electrode positioned external and proximate to the discharge electrodes for the purpose of generating a control electric field. This control electric field is able to vary the intensity of the plasma discharge and its spatial distribution by distorting the shape of the discharge electric field. In this and other similar devices, a degree of control over the properties of a plasma is exerted by an auxiliary device or structure, where “auxiliary” indicates that the added device or structure is not required for sustenance of the plasma. Soclof U.S. Pat. No. 4,683,399 summarizes typical prior devices that inject electrons into vacuum with a reverse-biased pn junction, and subsequently accelerate and collect the electrons with an anode.
Most commercially available displays are rigid and somewhat fragile. Despite these limitations, large displays such as flat panel TVs having screen sizes as large as >60″ have proven to be extremely successful. It is expected and would be desirable for the next generation of displays to be required to be lightweight (e.g., <100 g/ft2), manufacturable by inexpensive processes at sizes of 10 m2 and above (to full “wall size”) and, if possible, flexible. Existing large area LED displays are certainly bright but the cost is exorbitant (>$1 k per square foot) and such displays are certainly not flexible.
In U.S. Pat. No. 7,235,860, Ohki describes a solid state transistor in which the emitter is sub-divided into separate sub-emitters. However, the purpose of subdividing the emitter is only to increase emitter current while maintaining hfe. The emitters are electronically isolated from each other by an isolation region. Varying their surface area (i.e., the area exposed to the base) serves to control the maximum emitter current.